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The standard approach to obtaining knowledge about the properties of thesurface layer of a comet from observations of gas production consists of twostages. First, various thermophysical models are used to calculate gasproduction for a few sets of parameters. Second, a comparison of observationsand theoretical predictions is performed. This approach is complicated becausethe values of many model characteristics are known only approximately.Therefore, it is necessary to investigate the sensitivity of the simulatedoutgassing to variations in the properties of the surface layer. This problemwas recently considered by us for aggregates up to tens of microns in size. Formillimetre-size aggregates, a qualitative extension of the method used to modelthe structural characteristics of the layer is required. It is also necessaryto study the role of radiative thermal conductivity, which may play animportant role for such large particles. We investigated layers constructedfrom large aggregates and having various thicknesses and porosity and evaluatedthe effective sublimation of water ice at different heliocentric distances. Forradiative conductivity, approximate commonly used models and the complicatedmodel based on the Dense Medium Radiative Transfer theory were compared. It wasshown that for millimetre-size aggregates careful consideration of theradiative thermal conductivity is required since this mechanism of energytransfer may change the resulting gas productivity by several times. Wedemonstrate that our model is more realistic for an evolved comet than simplemodels parameterising the properties of the cometary surface layer, yetmaintains comparable computational complexity.

monthly notices of the royal astronomical society

Cometary surface dust layers built out of millimetre-scale aggregates:  dependence of modelled cometary gas production on the layer transport  properties